The present invention relates to retroreflective sheeting having a printed layer, particularly a triangular cube-corner retroreflective sheeting constituted of triangular cube-corner retroreflective elements (hereinafter also referred to simply as triangular reflective elements) which is characterized by having a printed layer for tone improvement in a part thereof and is useful for signs such as road signs and construction signs; license plates of vehicles such as automobiles and motorcycles; safety equipment such as garments and lifesaving equipment; markings of signboards; and reflectors such as visible light, laser light or infrared light reflective sensors; and the like.
Retroreflective sheeting which reflects incident light toward the light source has been well known. The sheeting having such retroreflective properties has been used widely in the above-described fields. In particular, cube-corner retroreflective sheeting making use of the retroreflection theory of cube-corner retroreflective elements such as triangular reflective elements and triangular cube-corner retroreflective sheeting having a vapor-deposition layer on the lateral faces of the triangular reflective elements thereof (hereinafter referred to as vapor-deposited triangular cube-corner retroreflective sheeting) are extremely superior in retroreflectivity to conventional retroreflective sheetings using micro glass beads and have been extending their use year by year because of their excellent retroreflective performance.
Such retroreflective sheetings and processes for producing them are described, e.g., in U.S. Pat. No. 3,417,959 and WO98/18028 as to triangular cube-corner retroreflective sheeting, and JP-A-49-106839 (U.S. Pat. No. 3,712,706) as to vapor-deposited triangular cube-corner retroreflective sheeting.
Vapor-deposited triangular cube-corner retroreflective sheeting has a disadvantage attributed to its retroreflective elements that the appearance is darkened by the influence of the metal color.
In order to improve the hue of the triangular cube-corner retroreflective sheeting and the vapor-deposited triangular cube-corner retroreflective sheeting, it has been attempted to provide a continuous printed layer in part of the retroreflective sheeting.
However, because a printed layer has slightly poor adhesion to both the reflective element layer and a surface protective layer and also has poor weatherability, it is liable to suffer lifting in a weathering test. It also has a disadvantage of easily absorbing water. Where a continuous printed layer is provided in a triangular cube-corner retroreflective sheeting or a vapor-deposited triangular cube-corner retroreflective sheeting, the sheeting has poor adhesion around the printed layer and poor weather resistance or water resistance.
In addition to the above-described triangular cube-corner retroreflective sheeting and vapor-deposited retroreflective sheeting, retroreflective sheetings include those using micro glass beads, such as encapsulated retroreflective sheeting and encapsulated lens retroreflective sheeting.
The encapsulated retroreflective sheeting comprises a light-transmitting support layer, a microbead layer provided opposite to the light incident side of the light-transmitting support layer in which a large number of micro glass beads are arrayed substantially in a monolayer with their almost semi-spherical portions being embedded, a light-transmitting focusing layer which is formed along the surface of the other non-embedded semi-spherical portions of the micro glass beads and has such a thickness that the micro glass beads may substantially focus on the surface of the focusing layer that is not in contact with the micro glass beads, and a light-reflective metal film which is formed on the surface of the focusing layer that is not in contact with the micro glass beads. If necessary, the sheeting can have a light-transmitting surface protective layer superposed on the surface of the light-incident side of the support layer.
The encapsulated lens retroreflective sheeting comprises a light-transmitting coating layer, a support layer, a lens retroreflective element layer provided on the surface of the support layer which faces the light-transmitting coating layer in which a large number of micro glass beads are arrayed substantially in a monolayer with their almost semi-spherical portions being embedded and with the embedded semi-spherical portions being coated with a light-reflective metal film, and an air layer provided between the light-transmitting coating layer and the lens retroreflective elements. The air layer is formed by partly connecting the light-transmitting coating layer and the support layer via joints such that gaps are formed between these layers, and the air layer is partitioned by the joints into a large number of closed small vacant spaces.
The encapsulated retroreflective sheeting and the encapsulated lens retroreflective sheeting essentially have lower retroreflective performance than the triangular cube-corner retroreflective sheeting or the vapor-deposited triangular cube-corner retroreflective sheeting. Therefore, where a printed layer is provided, they are incapable of satisfying the requirement for retroreflective performance.
In the light of the disadvantages of the conventional techniques, the present invention provides retroreflective sheeting with an improved hue by a very simple and inexpensive method.
The inventors of the present invention have conducted extensive investigation on hues of triangular cube-corner retroreflective sheeting or vapor-deposited triangular retroreflective sheeting. As a result, they have found that disposing a specific printed layer on the reflective element layer or the surface protective layer of the retroreflective sheeting provides retroreflective sheeting with excellent weather resistance and water resistance and an improved hue and thus have completed the present invention.
The present invention provides retroreflective sheeting having a printed layer which comprises at least a reflective element layer made up of a large number of reflective elements and a holding body layer and a surface protective layer provided on the reflective element layer, which is characterized in that the printed layer is provided in the lateral faces of the reflective elements or between the holding body layer and the surface protective layer or on the surface protective layer, the printed layer is formed of a discrete repetitive pattern of unit patterns, and the unit patterns each have an area of 0.15 mm2 to 30 mm2.